Color theory is a term used to describe the collection of rules and guidelines regarding the use of color in art and design, as developed since their early days. Color theory informs the designer of color schemes, aiming at aesthetic appeal and the effective communication of a 'design message' on both the visual level and the psychological level (also: Color temperature is another vital consideration in design).
Modern color theory is heavily based on Isaac Newton's color wheel, which displays three categories of colors: primary colors (red, yellow, blue), secondary colors (created by mixing two primary colors), and intermediate or tertiary ones (created by mixing primary and secondary colors). Colors can be combined to form one of the five main color schemes that allow designers to achieve harmony in their designs (as is noted at the bottom of this page).
When designing this page I used w3.css (w3schools.com) and other ideas from that website. Then I thought about it. - This is the result.
The future is not going to stand still. So there is a need to keep up with what is going on - the time to do so was found(COVID-19).
Dimensionalized.com 
Paul Glover
Here I am on Vancouver Island, (been here for awhile now but since COVID-19) & stuck at home more often now. So I'm updating my old skills.
I started working these pages about March 2020 and
since then they are being updated as shown: Nov/19/2021
3 Color Theories: RYB, RGB, CMY(K). + Color Combinations: Monochromatic, Analogous, Complementary, Triadic, Split Complementary, Tetradic, Square.
The RYB Color Wheel
There's lots of information on color ...
from many, color logical ways of thinking!
This div box is using a CSS gradient:
background:
linear-gradient(to bottom, #33ccff 0%, #ff99cc 100%);
There's lots of information on color ...
from many color logical ways of thinking!
Gradients can be produced (like this one) at w3schools.com.
So, speaking of gradients and color combinations, there is much information on how to choose a good color scheme.
. . .
The RGB Color Wheel of light ...
The RGB (Red, Green, Blue) color wheel represents
the 3 light sources used to produce colors on a TV or computer screen.
By mixing primary colors (R,G,B):
Red and Green= Yellow
Green and Blue = Cyan
Blue and Red = Magenta
The CMYK model works by partially or entirely masking colors on a lighter, usually white, background. The ink reduces the light that would otherwise be reflected. Such a model is called subtractive because inks "subtract" the colors red, green and blue from white light. White light minus red leaves cyan, white light minus green leaves magenta, and white light minus blue leaves yellow.
. . .
.. not only explains Color, but also
CSS (Cascading Style Sheets) when viewing source code.
The background gradient for this box stretches
all the way to the bottom, as more information is added.
In additive color models, such as RGB, white is the "additive" combination of all primary colored lights, while black is the absence of light.
In the CMYK model, it is the opposite: white is the natural color of the paper or other background, while black results from a full combination of colored inks.
To save cost on ink, and to produce deeper black tones, unsaturated and dark colors are produced by using black ink instead of the combination of cyan, magenta, and yellow.
. . .
Monochromatic schemes
use different tones from the same angle on the color wheel (the same hue).
Analogous color schemes
are created by using colors that are
next to each other on the color wheel.
Complementary schemes
are created by combining colors from
opposite sides of the color wheel.
Triadic schemes are made up of hues equally spaced around color wheel.
Compound schemes are almost the same as complementary schemes.
Instead of using colors that are opposites,
it uses colors on both sides of the opposite hue.
Tetradic or double complementary colors uses four colors together, in the form of two sets of complementary colors.